ABSTRACT Rheumatoid arthritis (RA) is associated with a 2-fold increased risk of cardiovascular disease (CVD), which is not explained by traditional cardiovascular (CV) risk factors alone; this risk is likely mediated in part through systemic inflammation. Indeed, RA itself is deemed to impart a CV risk equivalent to diabetes mellitus (DM). However, unlike in DM, optimal CV management strategies in RA are lacking. Despite improved anti- inflammatory therapies for RA, the mortality gap in RA compared to the general population is still widening, in part due to suboptimal primary and secondary CV preventive care in RA. To date, there have been no published controlled intervention trials for primary CV prevention in RA, despite this clearly urgent unmet need. One of the early stages of atherogenesis is endothelial dysfunction, and drugs that target improvement in this are promising novel strategies for CVD prevention. The fundamental feature of endothelial dysfunction is impaired nitric oxide (NO) bioavailability. Sildenafil improves endothelial function by increasing NO signaling by inhibition of phosphodiesterase-5 (PDE5). PDE5 inhibitors improve endothelial function in pulmonary hypertension and DM, and were safe and well tolerated in patients with erectile dysfunction and other CV comorbidities. Furthermore, PDE inhibitors have immunomodulatory properties that may be utilized to treat autoimmune conditions like RA. Our central hypothesis is that sildenafil is a uniquely suited agent targeting endothelial dysfunction as a novel adjunctive CV prevention strategy and immunomodulatory agent in RA. Specifically, our goal is to determine if sildenafil use in RA improves endothelial dysfunction and atherosclerosis biomarkers. The proposed study is a phase II, randomized double-blind placebo-controlled crossover efficacy trial of 60 RA patients, with no known history of CVD but at least one traditional CV risk factor, on stable baseline doses of RA medications; randomized 1:1 to receive either sildenafil 50 mg or placebo orally once daily for 3 months, with a 2-week washout before the crossover phase for another 3 months. Vascular studies validated in assessing endothelial dysfunction and laboratory studies for selected atherosclerosis biomarkers will be performed at baseline, 3 months pre- and post-washout, and 6 months. Adverse events will be collected to assess safety. Our Specific Aims are: 1. To determine whether sildenafil use in RA leads to improvement in parameters of vascular function; and to confirm its safety profile. 2. To determine whether sildenafil use in RA is associated with improvement in atherosclerosis biomarkers. The results of this study will serve as preliminary data for future larger trials evaluating sildenafil as a CV prevention strategy by reducing endothelial dysfunction in RA. It will provide needed data on potential benefits of sildenafil for immunomodulation and CV prevention in this high-risk population.